This has to do with the changes I made to Magick.NET. I am no longer using Fasterflect and moved all the 'architecture dependent' code to a separate library. I am referencing this library in the project but I am not including it in the output. When that
assembly is being resolved in your code it will not find it and it will use the embedded assembly. With Fasterflect this was all done with reflection so there was no missing reference.

Well, it seems that GAC is not the right place for such a library! :) It's just that the size of ImageMagick is pretty singificant (>12 MB), multiplied for a growing number of sites... mmm I'll see! Thanks again for the support!